1. Field of the Invention
This invention relates to an apparatus for drying a web of paper emerging from a press section of a papermaking machine. More particularly, this invention relates to an apparatus for drying a web in which the web is transferred without open draw between dryer sections, thereby permitting threading of the web without the assistance of threading ropes and the drying of both sides of the web.
2. Information Disclosure Statement
With the ever increasing operational speed of papermaking machines a serious problem has existed in that there is a tendency for the paper web or sheet to flutter as the sheet progresses through the dryer section. Such sheet flutter is particularly evident when the sheet is transferred between succeeding sections of the dryer section as the web is transferred between these adjacent sections in an open draw. Such sheet flutter has been minimized by the use of single felting configurations in which the web and felt run jointly between respective top and bottom cylinders. However, the single felt configuration, although reducing the aforementioned problem of sheet flutter, introduces several disadvantages. Included amongst these disadvantages are, first, the heat transfer from the bottom cylinders is substantially reduced because the wet web is no longer in direct contact with the cylinders, the felt being interposed between the web and the drying surface of the respective cylinder. Second, the web has a tendency to separate from the felt as the web travels towards and around and then away from the bottom cylinder. Third, the initial threading of the web is not particularly easy.
A partial solution to the aforementioned single felt problems has been provided by the application of the so-called Bel Run dryer section. Bel Run is a registered trademark of Beloit Corporation. With the Bel Run system, the bottom ineffective dryers are replaced by vacuum rolls which positively convey the web from one cylinder to the next. Recent installations of this type of dryer section have shown that the Bel Run concept can be extended to include a large number of dryers without any adverse effect on the web runability. Such runability results because the vacuum rolls are capable of conveying the web along the felt supported spans without the need for sheet tension or section draw points.
With the implementation of the single Bel Run section there exists a tendency to have a generation of stresses which develop in the web as the web dries. Such stresses impart a tendency for the dried paper to curl. Such adverse curling effect can be minimized or eliminated by drying the web from both sides, but two sided drying requires a transfer point in which the web is transferred from one felt to another felt. In the case of the Bel Run configuration, the web must be alternately dried on a top tier dryer section and then on a bottom tier dryer section. A top tier section may be defined as a group of dryers in which the bottom surface of the web contacts the dryers. A bottom tier section conversely and correspondingly may be defined as a group of dryers in which the top surface of the web contacts the dryers.
In order to efficiently transfer the web from one Bel Run section to another, a positive transfer arrangement is required. In the prior art such means for transferring the web from one drying section to the next has required the introduction of an open draw with the associated problems of sheet flutter and the like.
Modern paper drying machines are contemplated in which web speeds of 10,000 or more feet per minute are invisaged. Consequently, the introduction of such open draws would lead to serious problems of sheet flutter and numerous web breakages. The present invention seeks to overcome the aforementioned inadequacies of the prior art apparatus and to provide a drying apparatus which contributes a significant and non-obvious contribution to the paper drying art.
Another object of the present invention is the provision of an apparatus for drying a web of paper emerging from a press section of a papermaking machine such that the web is transferred between a first and a second dryer section means without open draw, thereby permitting both threading of the web without the assistance of threading ropes and the drying of the web on both sides thereof. Another object of the present invention is the provision of an apparatus for drying a web of paper which completely eliminates the need of open draws.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which open draws for the sheet or web is eliminated.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which blow boxes would be redundant.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which ventilation of the pockets defined by the cylinders and the vacuum rolls is improved, thereby improving the drying rate of the web.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which gear case leaks are inhibited and removal of broke is facilitated.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which fewer steamfits are required and none of the dryers are redundant, thereby reducing the blow through rate.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which the frame is symmetrical and in which the base frame is subjected to equal loading forces, thereby resulting in sturdy low-profile frame which reduces vibration and its attendant noise level.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which the power required to drive the cylinders is reduced and due to the layout and configuration of the dryers, such arrangement lends itself to the provision of a low-profile hood.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which runability of the drying apparatus is increased and in which doctors can be applied to each dryer.
Another object of the present invention is the provision of an apparatus for drying a web of paper which permits automatic threading of a tail and subsequent web therethrough.
Another object of the present invention is the provision of an apparatus for drying a web in which open access to the dryers and vacuum rolls is provided and a supply of air can be fed uniformly through each of the vacuum rolls.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which hoods are provided over and adjacent the vacuum rolls for handling the humid exhaust and possibly eliminating the need for large scale exhaust hood construction.
Another object of the present invention is the provision of an apparatus for drying a web of paper in which such vacuum roll hoods can be provided for profiling the web by removing exhaust air from selected transfer sections of these hoods.
Other objects and advantages of the present invention will be apparent to those skilled in the art by a consideration of the following detailed description taken in conjunction with the annexed drawings.
Although, the detailed description and annexed drawings describe a preferred embodiment of the present invention, it should be appreciated by those skilled in the art that many variations and modifications of the present invention fall within the spirit and scope of the present invention as defined by the appended claims.